1. Field of the Invention
The present invention relates to a method of optimizing an operation schedule of a plant and a system therefore, the method and system calculating an optimized operation schedule, including the startup and shutdown, of the plant or an item in the plant.
2. Description of the Related Art
Various operation management systems using optimized-operation scheduling methods or optimal control methods are suggested for power plants, including combined cycle power plants, thermal power plants, and atomic power plants, and the items in the power plants in order to optimize the economic efficiency or the operation efficiency.
The operation management systems include an operation schedule optimization method using a model predictive control disclosed in Non-patent Document 1 described below. In this method using the model predictive control, a control algorithm that allows for the dynamic characteristic model, the future desired value (operation planned value), and the operation constraints of a plant to be controlled to calculate an optimized manipulation signal sequence having a minimum evaluation function is adopted.
FIG. 9 is a diagram schematically showing the structure of a model predictive control method used in a known operation management system. This operation management system applies the manipulated variable and the controlled variable of a plant or system, to be controlled, to the predictive model so as to perform the optimization calculation and optimizes the operation of the plant in the basis of the predicted response.
Japanese Unexamined patent application Publication No. 2002-300720 (Patent Document 1) discloses an optimization mechanism allowing for the startup and shutdown of an electric generator, which is an item in a plant. The constraints, including the startup time constraint and the shutdown time constraint, relating to the startup and shutdown of the electric generator are considered in this optimization mechanism, and parameters in which the constraints, the fuel cost, the startup cost, the shutdown cost, and others are consolidated are included in a physical model to determine the startup and shutdown plan of the electric generator by optimization calculation so as to minimize the operation cost, including the amount of fuel, of the electric generator.
Upon startup and shutdown of a power plant or an item in the power plant, for example, a physical-model-based optimization method disclosed in Japanese Unexamined Patent Application Publication No. 8-128305 (Patent Document 2) is adopted. In this optimization method, the plant life is considered and a startup and shutdown operation pattern requiring a minimum time is determined by solving a physical-model-based nonlinear optimization equation based on the thermal stress control conditions affecting the plant item.
In such operation management systems, various optimization methods introduced in Non-patent Document 2 described below are adopted in the optimization calculation for optimizing the operation of a plant or an item in the plant, and an integer programming method and a mixed integer programming method introduced in Non-patent Document 3 described below are used in an operation schedule optimizing equation allowing for the startup and shutdown of a plant or an item in the plant.
Non-patent Document 1: Masahiro Ohshima and Morimasa Ogawa, “Model Predictive Control -I” Systems, Control and Information 46(5) 2002: 286–293
Non-patent Document 2: Toshihide Namiki and Masao Fukushima, Saitekika no Shuho (Kyoritsu Shuppan 2001), I (5–34) and IV (105–143)
Non-patent Document 3: Hiroshi Konno and Hisatoshi Suzuki, Seisukeikakuho oyobi Kumiawase Saitekika (Nikkagiren 1999) IV (49–80)
Since the manipulated variables (independent variables) are the continuous quantity determining the operating conditions of a plant in the operation schedule optimization method using a known model predictive control disclosed in Non-patent Document 1, optimized scheduling allowing for the event behavior, such as the startup and shutdown, of the plant is not realized.
An preparation device of a startup and shutdown plan of a generator, disclosed in Patent Document 1, performs the optimization allowing for the startup and shutdown constraints of the generator. In this optimization, the operation method upon startup and shutdown of the plant (generator) is determined by optimization calculation using model parameters in which the startup and shutdown constraint times are consolidated. Although an optimized operation pattern is determined based on the physical constraints, such as security, safety operation, thermal stress, and material strength, of a plant item when the plant is actually started up, the physical constraints are not considered in the Patent Document 1. Accordingly, the device disclosed in Patent Document 1 is not suitable for the operation method upon startup of the plant.
Furthermore, in a system and method of controlling startup of a thermal plant, disclosed in Patent Document 2, the plant is started up while determining the startup pattern by optimization calculation using a detailed physical model. Hence, a enormous amount of calculation is required in the system and method and it is difficult to rapidly start up the plant due to the long calculation time.